1. Field of the Invention
The invention relates to an actuating device for a friction clutch arranged in the drive train of a motor vehicle, in particular a commercial motor vehicle, between an internal combustion engine and a gear unit. The actuating device includes a disengagement bearing arrangement for actuating the friction clutch, and a positioning servo arrangement with a pressure-medium power cylinder arrangement which acts on the disengagement bearing arrangement and which is capable of being actuated, via a control valve connected to a pressure-medium source, as a function of a command quantity representing a desired position and of an actual quantity representing a position of the disengagement bearing arrangement. The control valve comprises a valve arrangement which is capable of being adjusted between a first control state connecting the pressure-medium power cylinder arrangement to the pressure-medium source and a second control state connecting the pressure-medium power cylinder arrangement to a first pressure compensating orifice. The valve arrangement is capable of being changed over between the two control states as a function of the actual quantity and of the command quantity, preferably as a function of a differential quantity assigned to the actual quantity and to the command quantity.
2. Description of the Prior Art
An actuating device of this type is known, for example, from German reference DE 197 16 600 A1, to which reference is made as xe2x80x9creference document 1xe2x80x9d and the disclosure content of which is incorporated herein by reference. Further actuating devices of this type are known from German reference DE 197 16 641 A1 (reference is made to this as xe2x80x9creference document 2xe2x80x9d), German reference DE 197 14 226 A1 which corresponds to U.S. Pat. No. 5,950,788 (reference is made to this as xe2x80x9creference document 3xe2x80x9d) and German reference DE 198 00 232 A1 (reference is made to this as xe2x80x9creference document 4xe2x80x9d). The disclosure of reference documents 2, 3 and 4 is likewise incorporated by reference in the disclosure of the present invention description.
Irrespective of the design of the control valve (reference documents 1 to 4 disclose various possibilities for designing the positioning servo arrangement and the control valve), it was shown that the positioning behavior of actuating devices of this type is unsatisfactory in many respects. Thus, there needs to be an improvement in the positioning accuracy and in the response behavior along the lines of a more direct response. In particular, there was shown to be a hysteresis behavior of the positioning servo arrangement in the assignment of the desired position and actual position, with so-called xe2x80x9cplay during extensionxe2x80x9d and xe2x80x9cplay during retractionxe2x80x9d (generally a regulating travel play). The time response behavior of the known positioning servo arrangements also could not satisfy all requirements. The limitations in the performance of the known actuating device would seem to be attributable at least partially to static friction and sliding friction in the disengagement bearing arrangement and/or the pressure-medium power cylinder arrangement and/or between components, moved relative to one another, of the control valve or, in general, of the positioning servo arrangement and are also reflected in the magnitude of a minimum regulating increment which the positioning servo arrangement has and which does not satisfy all requirements.
By contrast, an object of the present invention is to provide an actuating device of the type initially mentioned, which allows improvements to the problems mentioned. In order to achieve this object, it is proposed that there be provided, in a pressure-medium subsystem comprising the pressure-medium power cylinder arrangement and the control valve, a second pressure compensating orifice which, at least when the positioning servo arrangement is in a holding state, permits a defined second pressure-medium pressure compensating flow smaller than a first pressure-medium pressure compensating flow permitted by the first pressure compensating orifice in the second control state, in order to influence at least one positioning behavior of the positioning servo arrangement.
To be precise, it was shown, surprisingly, that a measure which per se is extremely simple, namely the provision of a defined leak in said pressure-medium subsystem, for example in the pressure-medium power cylinder arrangement and/or in a pressure-medium connection connecting the control valve to the pressure-medium power cylinder arrangement and/or in a portion of the control valve located on the same side as the pressure-medium power cylinder arrangement, is sufficient to influence the positioning behavior of the positioning servo arrangement for adaption to requirements to be fulfilled. It is possible, for example, for a response behavior of the positioning servo arrangement to be improved, for example to the effect of reducing an idle time assigned to the positioning servo arrangement. Furthermore, it is possible, by means of the second pressure compensating orifice, to reduce a minimum regulating increment of the positioning servo arrangement and/or to reduce a regulating error of the positioning servo arrangement. It is particularly important, for many driving situations, that the second pressure compensating orifice can act with the effect of reducing a regulating hysteresis of the positioning servo arrangement and/or can reduce a regulating travel play of the positioning servo arrangement.
According to current knowledge, the observed modification, particularly the improvement in the response behavior of the positioning servo arrangement by means of the second pressure compensating orifice, is independent of the design of the positioning servo arrangement and especially of the control valve in particular. For example, the valve arrangement of the control valve may be capable of being adjusted as a function of the differential quantity into a third control state, in which the pressure-medium power cylinder arrangement is not connected either to the pressure-medium source or to the first pressure compensating orifice. Also, according to current knowledge, the modification or improvement in the response behavior by means of the second pressure compensating orifice is independent of the operating principle of the positioning servo arrangement and especially of the control valve.
In general, it is proposed that, in the case of a valve arrangement capable of being adjusted into the third control state, the second pressure compensating orifice permits the second pressure-medium pressure compensating flow in the third control state and preferably in the first control state and/or in the second control state, and that, in the case of a valve arrangement capable of being adjusted only between the first control state and the second control state, the second pressure compensating orifice permits the second pressure-medium pressure compensating flow at least in the first control state, preferably in the first control state and in the second control state.
The pressure medium may be a hydraulic or pneumatic pressure medium. In the case of a hydraulic pressure medium, the pressure-medium source is then in the form of a hydraulic source. In the case of a pneumatic pressure medium, the pressure-medium source is in the form of a pneumatic source. A pneumatic overpressure source is intended, in particular, here, which discharges a pressure higher than ambient pressure. However, a pneumatic underpressure source also comes under consideration, which serves for generating in the pressure-medium power cylinder arrangement an underpressure which is lower than ambient pressure.
It was possible to show the effectiveness of the idea of the invention, in terms of influencing and optimizing the positioning behavior of the positioning servo arrangement, by means of various positioning servo arrangements, especially by means of various control valves. Furthermore, it was possible to demonstrate the effectiveness of the idea of the invention by means of an electrically activated proportional valve, to which the desired value and the actual value detected by a displacement transducer were supplied electrically. A control valve of this type comprises at least one electromagnetically adjustable valve element, for example at least one solenoid-actuable valve element.
In order, for many operating states, to reduce a pressure-medium loss caused by the second pressure compensating orifice, the second pressure compensating orifice may be capable of being selectively activated and deactivated. The pressure-medium power cylinder arrangement is preferably a single-acting pressure-medium power cylinder arrangement which cooperates, for example, with a spring arrangement, for example a diaphragm spring of the friction clutch, said spring arrangement being assigned to the disengagement bearing arrangement. However, the pressure-medium power cylinder arrangement may also be a double-acting pressure-medium power cylinder arrangement. It is proposed, for this purpose, that the second pressure compensating orifice be assigned or may selectively be assigned a pressure-medium chamber, assigned to a disengagement of the friction clutch, or a pressure-medium chamber, assigned to an engagement of the friction clutch, of the pressure-medium power cylinder arrangement. Alternatively, it is possible that the pressure-medium chamber assigned to engagement and the pressure-medium chamber assigned to disengagement be assigned in each case its own second pressure compensating orifice capable, if desired, of being selectively (preferably reciprocally) activated and deactivated.
In general, in light of the desired positioning behavior, the second pressure compensating orifice should have a flow cross section which is coordinated with a narrowest flow cross section (supply flow cross section) in the pressure-medium system connecting the pressure-medium source to the pressure-medium power cylinder arrangement and/or with a cylinder volume (if appropriate, a cylinder volume range) of the pressure-medium power cylinder arrangement and/or with a characteristic pressure-medium pressure level prevailing in the pressure-medium power cylinder arrangement when the positioning servo arrangement is in an actuating state, for example in order to achieve a desired driving behavior of the motor vehicle, preferably a desired maneuvering behavior of the motor vehicle.
For many practical situations and designs of the actuating device, in the case of a pneumatic pressure medium a flow cross section of about 0.4 mm to about 0.8 mm, preferably of about 0.6 mm, of the pressure compensating orifice would seem to be advantageous, for example in conjunction with a cylinder volume of about 0.3 l to about 0.8 l and a narrowest supply flow cross section of about 4 mm to about 10 mm, preferably of about 7 mm, and/or a pneumatic pressure which, when the positioning servo arrangement is in an actuating state, is in the range of about 2.5 to about 3.5 bar in the pressure-medium power cylinder arrangement designed as a pneumatic power cylinder arrangement. In the case of a different cylinder volume and/or in the case of a different narrowest supply flow cross section and/or in the case of a different pneumatic pressure range, the flow cross section of the second pressure compensating orifice may be adapted, preferably in such a way that a corresponding positioning behavior is achieved.
The second pressure-medium pressure compensating flow may profitably be used for other purposes, for example as a cooling flow or dust protection flow. The first pressure compensating flow may be used correspondingly. It is accordingly proposed that guide means be provided for guiding the second and/or the first pressure compensating flow to at least one assigned point of the actuating device, the friction clutch or the motor vehicle, in order to serve at the assigned point as a treatment flow and/or auxiliary flow, for example as a cooling flow or dust protection flow. The idea of which is independent of the presence or absence of a second pressure compensating orifice. It would also be conceivable to provide, instead of a pressure compensating flow interrelated with the functioning of the positioning servo arrangement, a pressure-medium flow which serves, uncited, as a treatment flow and/or auxiliary flow and which is provided by the pressure-medium system and is not necessarily interrelated with or does not necessarily influence the functioning of the positioning servo arrangement. The idea of this embodiment is accordingly independent of the functioning and makeup of the actuating device; it is sufficient, in principle, that the actuating device have a pressure-medium power cylinder arrangement capable of being connected to a pressure-medium source.
The invention relates furthermore, in general terms, to an actuating and/or positioning device, comprising a servo arrangement with a pressure-medium power cylinder arrangement which acts on at least one element to be actuated and/or to be positionable and which is capable of being actuated, via a control valve connected to a pressure-medium source, as a function of a command quantity representing a desired position or a desired actuating state and of an actual quantity representing an actual position or an actual actuating state of the element. The control valve comprises a valve arrangement which is capable of being adjusted between a first control state connecting the pressure-medium power cylinder arrangement to the pressure-medium source and a second control state connecting the pressure-medium power cylinder arrangement to a first pressure compensating orifice and is capable of being changed over between the two control states as a function of the actual quantity and of the command quantity, preferably as a function of a differential quantity assigned to the actual quantity and to the command quantity.
There is provision, according to the invention, for providing, in a pressure-medium subsystems comprising the pressure-medium power cylinder arrangement or the control valve, a second pressure compensating orifice which, at least when the servo arrangement is in a holding state, permits a defined second pressure-medium pressure compensating flow smaller than a first pressure-medium pressure compensating flow permitted by the first pressure compensating orifice in the second control state, in order to influence at least one positioning and/or actuating behavior of the servo arrangement. The actuating and/or positioning device may have further features of the above-described actuating device relating to a friction clutch, the positioning servo arrangement corresponding to the servo arrangement and the disengagement bearing arrangement corresponding to the element to be actuated and/or to be positioned.
The invention is explained in more detail below by means of several exemplary embodiments shown in the figures and by means of measurement results determined during tests.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.